However, Mr Juppé, 70, enjoys greater public support outside the party, according to polls.

Alain JuppéCredit:
Nicolas Tucat/AFP

Mr Sarkozy told members of Les Républicains on Saturday that he was stepping down as head of the Republican party.

Under party rules, Mr Sarkozy would be disbarred from running in the primary if he remains chairman.

Mr Juppé criticised him for exploiting that position to advance his candidacy.

“He has fostered confusion between Nicolas Sarkozy, party chairman, and Nicolas Sarkozy, candidate campaigning for the primaries,” Mr Juppé said.

The primary will also be open to members of other centre-Right parties.

The leader of the largest centrist group, François Bayrou, backs Mr Juppé.

If Mr Sarkozy wins the nomination, Mr Bayrou said he will withdraw the support of his MoDem party and enter the presidential race himself.

Mr Sarkozy called for a primary free from acrimony.

“This primary will be a time of competition between some strong personalities,” he said. “When the Right goes into battle, it has a front on the Left and a front on the extreme Right. That is why it is unacceptable that we should attack each other.”

The far-Right Front National leader, Marine Le Pen, is expected to reach the final round of voting in the presidential election next spring.